A sliding nozzle device is widely used in a molten metal vessel such as a ladle or a tundish, because of its advantage of being able to accurately control a flow rate of molten metal. The sliding nozzle device comprises: a fixed metal frame fixed to a bottom of a molten metal vessel; an opening-closing metal frame coupled to the fixed metal frame in an openable and closable manner; and a sliding metal frame installed to the opening-closing metal frame in a slidable manner, wherein two or three plates are attached and fixed to these metal frames, and a contact pressure is applied between the plates, whereafter the sliding metal frame is slidingly moved by a driving mechanism such as a hydraulic cylinder to thereby control a flow rate of molten metal during pouring. As the plate, a type in which a metal band, such as a strip or hoop made of a metal, is provided on a side (peripheral) surface of a plate-like refractory plate member having a nozzle hole, and an expansion absorbing material and a backplate are provided on a back surface of the refractory plate member, and a type in which the side surface and the back surface of the refractory plate member is covered by a box-shaped metal casing, are commonly used.
In such a sliding nozzle device, a technique of fixing the plate to a plate-receiving metal plate (which is a general term for the fixed metal frame, the opening-closing metal frame and the sliding metal frame; this is also applied to the following description) is toughly classified into two of the following. One is a technique of to fixing a plate by pressing a side (peripheral) surface thereof using a bolt, cotter or the like, thereby receiving a sliding force by such a fixing structure (e.g., the following Patent Document 1), and the other is a technique of fixing a plate by fitting together a fitting convex or concave portion provided in a back surface (non-sliding surface) of the plate, and a counterpart, fitting concave or convex portion provided in a plate-receiving metal frame, thereby receiving a sliding force by such a fixing structure (e.g., the following Patent Document 2). The term “back surface” of a plate means a surface of the plate on a side opposite to a sliding surface thereof capable of being slidingly moved with respect to another plate.
Generally, a plate is replaced with a new one after several usage cycles. During the replacement work, the plate-receiving metal frame is opened and set to extend vertically, and, in this state, the old plate is detached and then a new plate is attached. Thus, in the technique using a bolt or cotter, it is necessary for a worker to tighten the bolt or cotter with one of his/her hands, while holding the plate with the other hand so as not to drop off, so that there is a problem that it needs to take a lot of time and effort.
In the technique of fitting a plate into a plate-receiving metal frame as in the Patent Document 2, actually, it is also necessary to take a lot of time and effort. This is because, considering that an increase in gap between the fitting convex or concave portion of the plate and the fitting concave or convex portion of the plate-receiving metal frame in a sliding direction of the plate leads to deterioration in accuracy of adjustment of an opening degree of the nozzle hole, the gap is set to a small value of about 0.5 mm. That is, due to the small gap, it is difficult to achieve an alignment between the fitting convex or concave portion of the plate and the fitting concave or convex portion of the plate-receiving metal frame, or it is necessary to take a lot of time and effort for achieving the alignment. Moreover, the fitting convex portion and the fitting concave portion are located on the side of the back surface of the plate, so that a worker cannot perform position adjustment while visually checking them, which makes it more difficult to achieve the alignment.
The following Parent Document 3 describes a plate fixing technique which is based on the technique of fitting a plate into a plate-receiving metal frame as in the Patent Document 2, wherein a thin plate spring is provided between the plate and the plate-receiving metal frame. The Parent Document 3 mentions that, generally, in a process of fitting the plate into the plate-receiving metal frame, a worker first inserts a lower end of the plate into the plate-receiving metal frame to put a weight of the plate on the plate-receiving metal frame, and then pushes an upper end of the plate into the plate-receiving metal frame. However, this fixing technique also has a problem that it is difficult to achieve an alignment between a fitting convex or concave portion of the plate and a counterpart, fitting concave or convex portion of the plate-receiving metal frame, for the following reason.
The plate in the Patent Document 3 comprises a refractory plate member covered by a metal casing. While this metal casing is generally produced by drawing, dimensional accuracy of drawing is lower than those of other metal working processes. For example, in a large type of plate having a length of about 450 mm, a variation of about 1 mm per overall length occurs.
Further, during drawing of the metal casing, distortion occurs in the metal casing. Moreover, when the plate is pushed into the metal casing through mortar, the metal casing is likely to be expanded. For these reasons, it is difficult to obtain a side (peripheral) surface of the metal casing as a surface perpendicular to a sliding direction of the plate. Thus, when the plate is fitted into the plate-receiving metal frame while putting the lower end of the plate on the plate-receiving metal frame, it is difficult to obtain accuracy of the alignment (parallelism) between the fitting convex or concave portion of the plate (metal casing) and the fitting concave or convex portion of the plate-receiving metal frame.
As above, for the two reasons: low dimensional accuracy of the metal casing; and distortion/deformation of the metal casing, in the technique of simply inserting the lower end of the plate into the plate-receiving metal frame to put the weight of the plate on the plate-receiving metal frame and then pushing the upper end of the plate into the plate-receiving metal frame, a variation in relative position between the fitting convex or concave portion of the plate and the fitting concave or convex portion of the plate-receiving metal frame occurs, often resulting in failing to achieve the fitting between the plate and the plate-receiving metal frame. Moreover, it is conceivable that the metal casing is subjected to finish processing for ensuring dimensional accuracy and planar accuracy of the side surface. In this case, however, it is necessary to machine the entire metal casing, so that a finishing surface area becomes large, causing an increase in cost. It is also conceivable that a metal band is provided on a side (peripheral) surface of a refractory plate member without using the metal casing. In this case, however, dimensional accuracy becomes worse than that of the metal casing, because the refractory plate member is generally subjected to burning in a production stage, and resulting burning shrinkage causes a variation in the overall length.